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    <p><code>extends</code> is for <em>extending</em> a class.</p> <p><code>implements</code> is for <em>implementing</em> an interface</p> <p>The difference between an interface and a regular class is that in an interface you can not implement any of the declared methods. Only the class that "implements" the interface can implement the methods. The C++ equivalent of an interface would be an abstract class (not EXACTLY the same but pretty much).</p> <p>Also java doesn't support <strong>multiple inheritance</strong> for classes. This is solved by using multiple interfaces.</p> <pre><code> public interface ExampleInterface { public void doAction(); public String doThis(int number); } public class sub implements ExampleInterface { public void doAction() { //specify what must happen } public String doThis(int number) { //specfiy what must happen } } </code></pre> <p>now extending a class</p> <pre><code> public class SuperClass { public int getNb() { //specify what must happen return 1; } public int getNb2() { //specify what must happen return 2; } } public class SubClass extends SuperClass { //you can override the implementation @Override public int getNb2() { return 3; } } </code></pre> <p>in this case</p> <pre><code> Subclass s = new SubClass(); s.getNb(); //returns 1 s.getNb2(); //returns 3 SuperClass sup = new SuperClass(); sup.getNb(); //returns 1 sup.getNb2(); //returns 2 </code></pre> <p>I suggest you do some more research on <strong>dynamic binding, polymorphism and in general inheritance in Object-oriented programming</strong></p>
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    1. COAn interface can contain way more than method declarations: Constant fields, annotations, interfaces and even classes.
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    2. CO"can only specify methods." is pretty misleading...
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    3. COare they something like modules and mixins in ruby?
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